The trunk lids of many modern automobiles are counterbalanced by tension coil spring assemblies located within the trunk compartments of such vehicles. When the trunk lid of such vehicle is closed, the springs (ordinarily two, one on each side of the vehicle) are in stretched or tensioned condition. It has been observed that under such conditions, if any one of the passenger doors is firmly closed, the counterbalancing springs will vibrate causing an objectionable ringing or zinging sound. Such a sound tends to be transmitted throughout the vehicle body which functions as a sounding board.
Efforts to prevent or limit such free vibration of the tensioned springs when a vehicle's doors are closed (or when the vehicle is impacted in any other way as, for example, by closing the engine compartment lid or hood) have in the past been only partially successful at best. Thus, sound-dampening coating materials have been applied to such springs without producing any appreciable diminution of the ringing sound when such a spring is caused to vibrate. Rubber wedges have been fitted between such a spring and its connection to the auto body but with uneven results. In some cases the ringing sound is found to be diminished when the vehicle doors are forceably closed but such a sound is still generated when the trunk lid is opened, or closed, or both. A further disadvantage to such rubber parts is that such parts cannot be pre-mounted on the counterbalancing spring assembly, or cannot be put in place at the time the spring assemblies are attached, because at such a stage in the manufacture of the vehicle further painting and baking of the body are required. In general, such rubber components are incapable of withstanding the elevated temperatures used for baking automotive finishes.
An important aspect of this invention therefore lies in the discovery that suppressing the free vibration of a tensioned coil spring may be effectively accomplished by utilizing a second spring metal element in the form of a C-shaped sleeve that is coaxial with the coil spring and that tightly embraces an intermediate portion of that coil spring. Ideally, two such sleeves are used for each coil spring of a typical counterbalancing assembly for a vehicle trunk lid, and a greater number of sleeves may be used in other applications where coil springs of greater length are utilized. Such a sleeve may be easily snapped in place and, because of its spring metal construction, may easily withstand the elevated temperatures encountered in subsequent painting or other manufacturing steps. Stop means in the form of a lug portion projecting from the inner surface of the sleeve limits the extend of longitudinal sliding movement of the sleeve along the spring on which it is mounted.
The C-shaped sleeve is of circumferentially-interrupted cylindrical shape; that is, its inner and outer surfaces would be generally cylindrical if it were not for the longitudinal slit or opening that circumferentially interrupts such surfaces. The sleeve has an axial length substantially less than that of the coil spring extending through it. In general, the length of the spring sleeve is only a minor portion of the length of the coil spring in an untensioned state and, ideally, the length of the sleeve is no greater than its outside diameter (when untensioned). However, the sleeve must have an axial length equal at least to the axial length of one full coil of the spring when that spring is in its maximum state of tension in normal use. Also, when the spring-metal sleeve is in an undeformed state, its inside diameter should be appreciably less than the outside diameter of the cylindrical coil spring. In general, the sleeve should have an inside diameter within the range of 5 to 8% smaller than the outside diameter of the coil spring in an untensioned state. The angular dimension of the arcuate C-shaped spring should fall within the general range of 270.degree. to 310.degree., a preferred range being approximately 280.degree. to 300.degree..
Other features, advantages, and objects of the invention will become apparent from the specification and drawings.